Zoology 250

Clade for Phylum PORIFERA

PHYLUM PORIFERA (sponges; tree & traits from Ruppert/Barnes, Ed. #7) 

        ==2======== Hexactinellida (glass sponges; no regular canal system)
        |
        |========== Sclerospongia (coralline sponges; leucon type, silica & calcareous spicules)
<<===1==|
        |    ==4=== Calcarea (includes ascon, sycon & leucon grades)
        ==3==|
             ==5=== Demospongia (most living sponge species; leucon type)
TRAITS SUPPORTING EACH CLADE
(** plesiomorphic- a primitive state, not unique to clade):

1:
a) adult is sessile
b) water canal system with pumping choanocytes** (monociliated cells with diplosome)
c) extensive mesenchyme (gelatinous proteinaceous matrix containing skeletal material & amoeboid cells)
d) silica spicules, initiated intracellulary
e) pinacoderm (epithelium-like outer layer) lacking basal lamina & intercellular junctions
f) dynamic tissue remodelling (reversible differentiation of most cell types)
2:
a) silica spicules**
b) distinctive 6-pointed spicule (hexactine)
c) most cells part of extensive syncytium
3:
a) porocytes (pore cells)
b) transport of sperm to egg via choanocyte
4:
a) loss of silica spicules
b) calcareous spicules
5:
a) silica spicules**
b) spongocytes & spongin fibers
c) distinctive 4-pointed spicule (tetraxon)

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Copyright © 2000 by A. Richard Palmer. All rights reserved.
(revised Jan. 18, 2000)